Switch apparatus and mobile communications terminal apparatus

ABSTRACT

A small-sized switch apparatus for switching between signal paths of at least first, second and third frequency bands is capable of handling high-powered high-frequency signals with a relatively low control voltage and is useful in a mobile terminal apparatus. A first signal terminal of a diplexer is connected to an antenna terminal, and a second signal terminal is connected to a high-frequency switch via a filter. A third signal terminal of the diplexer is connected to a high-frequency switch via a second filter. The high-frequency switch has PIN diodes as switching devices, and performs switching between a global system for mobile communications transmission signal and a global system for mobile communications reception signal. The high-frequency switch has three sets of serially connected multi-staged FETs as switching devices, and performs switching between wide-band code division multiple access transmission/reception signals, a digital cellular system transmission signal and a digital cellular system reception signal.

TECHNICAL FIELD

The present invention relates to a mobile communications terminalapparatus, and more specifically, to a switch apparatus for use in amobile communications terminal apparatus for a multi-system, in whichvarious frequency bands and communications schemes are used, and forswitching between signal paths of at least three frequency bands.

BACKGROUND ART

In recent years, mobile communications has developed significantly, andin Europe, mobile communications terminal apparatuses (hereinafterreferred to simply as mobile terminals) using several frequency bandsand several communications schemes are proposed. For instance, there isUMTS (Universal Mobile Telecommunication System) which combines GSM(Global System for Mobile Communications) using a frequency band of 900MHz band, DCS (Digital Cellular System) using a frequency band of 1.8GHz and WCDMA (Wideband Code Division Multiple Access) using a frequencyband of 2 GHz.

Because UMTS needs to operate as a mobile terminal of a multi-systemwith differing frequency bands as well as communications schemes, thecircuitry thereof becomes complex, and the increase in the number ofcomponents causes the apparatus to become larger and an increase incost. For this reason, there is a need to reduce the number ofcomponents by integrating the circuitry, and to proactively share thecomponents. In particular, since facilitating the sharing of an antenna,which is large in size, greatly contributes to the miniaturization of aterminal, the development of a small-sized switch apparatus is now animportant issue in order to switch an antenna between systems.

As a conventional example, there is a switch apparatus for sharing anantenna using a diplexer and a high-frequency switch in a mobileterminal in which GSM and DCS are integrated. Switch apparatuses of thissort include the switch apparatus disclosed in Unexamined JapanesePatent Application No. 2000-183780, for instance.

The configuration of such a switch apparatus of the conventional exampleis shown in FIG. 4. An antenna, which resonates with the frequency bandsof both GSM and DCS, is connected to an antenna terminal T_(ant). A GSMreception circuit is connected to a GSM reception signal terminalT_(gsmrx). A GSM transmission circuit is connected to a GSM transmissionsignal terminal T_(gsmtx). A DCS reception circuit is connected to a DCSreception signal terminal T_(dcsrx). A DCS transmission circuit isconnected to a DCS transmission signal terminal T_(dcstx). A diplexer 1has the combined characteristics of a high-pass filter and a low-passfilter, and mutually separates signals of GSM and DCS with an isolationof approximately 20 dB. A filter 2 attenuates the higher harmonics of aGSM transmission signal. A high-frequency switch 4 switches betweentransmission and reception of GSM. A filter 3 attenuates the higherharmonics of a DCS transmission signal. A high-frequency switch 5switches between transmission and reception of DCS.

Here, PIN diodes are used for the high-frequency switches 4 and 5. ThePIN diodes come to be in an on state when forward-biased and theimpedance drops to approximately several Ω, and comes to be in an offstate of high impedance with an inter-terminal capacitance on the orderof several hundred fF. In general, in handling large power with a PINdiode, there is a higher probability of causing distortion in signalsduring transmission when it is in the off state.

In transmitting with GSM, a voltage of 3V is applied to controlterminals T_(ctl) 2 and T_(ctl) 3, and 0V is applied to T_(ctl) 1 andT_(ctl) 4. As a result, PIN diodes D1 and D2 come to be in the on state,and D3 and D4 come to be in the off state. Thus, it is turned on betweenthe GSM transmission signal terminal T_(gsmtx) and the filter 2, and theGSM transmission signal is transmitted to the antenna terminal T_(ant)via the high-frequency switch 4, the filter 2 and the diplexer 1.Although part of the GSM transmission signal reaches the high-frequencyswitch 5, because it is attenuated by 20 dB or more from 33 dB of theGSM standards, only approximately 13dBm is applied to the PIN diodes D3and D4 both in the off state, and no distortion occurs even with areverse-bias potential of a low voltage. In transmitting with DCS, avoltage of 3V is applied to the control terminals T_(ctl) 1 and T_(ctl)4, and 0V is applied to the control terminals T_(ctl) 2 and T_(ctl) 3,but otherwise an explanation of the operation would be the same as GSMtransmission.

Thus, the switch apparatus of the conventional example prevents theoccurrence of distortion at the PIN diodes in the off state by mutuallyseparating the transmission signals of GSM and DCS with the diplexer 1.It may be said that this is a configuration realizable with asmall-sized diplexer by virtue of the fact that the frequencies arewidely separated, GSM being in the 900 MHz band, and DCS in the 1.8 GHzband.

However, in order to make it possible to switch between WCDMA inaddition to GSM and DCS, because WCDMA is in the 2 GHz band and DCS isin the 1.8 GHz band, and the frequencies are close to each other, therearises a problem in that these two signals cannot be separated with asmall-sized diplexer.

Although a method of suppressing the occurrence of distortion byapplying a reverse-bias potential of a high voltage to a PIN diode isalso conceivable, it would become necessary to provide a voltagetransformer apparatus such as a DC-DC converter, and there arises aproblem in that the number of components and the cost increase.Therefore, this method is not suitable for a small-sized mobileterminal.

In addition, high-frequency switches such as the high-frequency switches4 and 5 which use PIN diodes have a problem in their structure such thatthey are difficult to expand for use in switching between signals of 3or more systems.

The present invention is provided in order to solve the this problem,and its object is to provide a small-sized switch apparatus capable ofhandling high-powered high-frequency signals with a relatively lowcontrol voltage, which switches between signals paths of at least afirst, second and third frequency bands, and a mobile terminal apparatususing same.

DISCLOSURE OF THE INVENTION

A switch apparatus according to the present invention is a switchapparatus for switching between signal paths of at least a first, secondand third frequency bands, and comprises a diplexer having a firstsignal terminal, which is a transmission/reception signal terminalcommon to the signals of at least the first, second and third frequencybands mentioned above, a second signal terminal for outputting thesignal of the first frequency band separated from a received signal, anda third signal terminal for outputting the remaining signal after thesignal of the first frequency band mentioned above is separated, whereinthe received signal to be inputted to the first signal terminalmentioned above is divided between the second and third signal terminalsmentioned above, and transmission signals inputted to the second andthird signal terminals mentioned above are combined and outputted to thefirst signal terminal, a first high-frequency switch connected to theaforesaid second signal terminal of the diplexer, and a secondhigh-frequency switch connected to the aforesaid third signal terminalof the diplexer, and is characterized in that the first high-frequencyswitch mentioned above has a plurality of switching means respectivelyconfigured with diodes, and is configured such that two signal terminalsare selectively switched and connected to the aforesaid second signalterminal of the diplexer, and the second high-frequency switch has atleast three switching means respectively configured with FETs, and isconfigured such that at least three signal terminals are selectivelyswitched and connected to the third signal terminal of the diplexermentioned above.

As described above, in handling signals of at least three frequencybands, first, a signal of one frequency band and signals of otherfrequency bands are divided, and the signal in which signals of severalfrequency bands coexist are handled with at least three switching meansin the second high-frequency switch, without increasing the size of thediplexer. The second high-frequency switch comprising at least the threeswitching means can be made a simple circuit configuration employing arelatively small number of components by being configured with FETsinstead of diodes.

In addition, by connecting each of the switching means of the secondhigh-frequency switch in series and in multiple stages, even when atransmission signal of a different frequency band, which does not passthrough the diplexer in the second high-frequency switch, is appliedwithout being attenuated, the FETs in the off state are not turned oneven with low reverse-bias potentials, and the occurrence of distortionmay be prevented.

On the other hand, by having the first high-frequency switch comprisediodes, when switching between the two signal terminals, both diodes aresimultaneously turned on at signal transmission. (Both diodes aresimultaneously turned off at signal reception.) Thus, the problem ofdistortion during the off state of the switching devices does not ariseat signal transmission in the first high-frequency switch. As regardsthe relation with the second high-frequency switch, because the diplexercomes in between, the problem of distortion, again, does not arise.

In the switch apparatus above, the signals of the first, second andthird frequency bands, for example, are GSM, WCDMA and DCS signals,respectively.

The mobile communications terminal apparatus according to the presentinvention may be configured by connecting the first signal terminal ofthe diplexer of the switch apparatus having the configuration mentionedabove to the antenna, connecting the transmission/reception circuit forthe signal of the first frequency band mentioned above to the two signalterminals of the first high-frequency switch mentioned above, andconnecting the transmission/reception circuit for the signals of thesecond and third frequency bands mentioned above to at least the threesignal terminals of the second high-frequency switch mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of a switchapparatus which is one mode for carrying out the present invention;

FIG. 2 is a diagram which illustrates as a table the status of thecontrol signal of each switching device of the switch apparatus of FIG.1 and the corresponding switching status;

FIG. 3 is a block diagram showing the configuration of a switchapparatus of a second mode for carrying out the present invention; and

FIG. 4 is a block diagram showing the configuration of a switchapparatus of a conventional example.

BEST MODES FOR CARRYING OUT THE PRESENT INVENTION

Modes for carrying out the present invention will now be described indetail below.

FIG. 1 shows the configuration of a switch apparatus of one mode forcarrying out the present invention. In this drawing, like elements shownin FIG. 4 are designated by like reference numerals. An antenna, whichresonates with the frequency bands of WCDMA, DCS and GSM, is connectedto an antenna terminal T_(ant). A GSM reception circuit is connected toa GSM reception signal terminal T_(gsmrx). A GSM transmission circuit isconnected to a GSM transmission signal terminal T_(gsmtx). A DCSreception circuit is connected to a DCS reception signal terminalT_(dcsrx). A DCS transmission circuit is connected to a DCS transmissionsignal terminal T_(dcstx). A WCDMA transmission/reception circuit isconnected to a WCDMA transmission/reception signal terminal T_(wcdma).The reason only WCDMA is transmission/reception is because transmissionand reception are simultaneously performed since the duplex operationscheme of WCDMA is FDD (Frequency Domain Duplex).

As described above, a diplexer 1 has the combined characteristics of ahigh-pass filter and a low-pass filter. In the configuration of FIG. 1,the diplexer 1 has a first signal terminal which is connected to theantenna terminal T_(ant), a second signal terminal which is connected toa filter 2 and a third signal terminal connected to a filter 3. WCDMAand DCS signals pass through the high-pass filter of the diplexer 1, GSMsignals pass through the low-pass filter of the diplexer 1, both signalsare mutually separated with an isolation of approximately 20 dB. Thefilter 2 attenuates the higher harmonics of the GSM transmission signal.The filter 3 attenuates the higher harmonics of the WCDMA and DCStransmission signals. A high-frequency switch 4 is controlled such thatit conducts one of the GSM transmission signal and a reception signal. Ahigh-frequency switch 50 is controlled such that it conducts one of theDCS transmission signal, reception signal and the WCDMAtransmission/reception signal.

The high-frequency switch 4 as used herein has the same configuration asthe high-frequency switch 4 shown in FIG. 4 and uses PIN diodes asswitching devices. As described above, when the PIN diodes areforward-biased, the impedance falls to approximately several Ω and theycome to be in an on state, and when reverse-biased, they come to be inan off state of a high impedance with an inter-terminal capacitance onthe order of several hundred fF.

On the other hand, for the high-frequency switch 5, field effecttransistor FETs, more specifically in this case, GaAs (gallium arsenide)FETs, are used as the switching devices. In other words, seriallyconnected FETs 31, 32 and 33, serially connected FETs 21, 22 and 23 andserially connected FETs 11, 12 and 13 are respectively inserted betweenthe filter 3 and each of the signal terminals the WCDMAtransmission/reception signal terminal T_(wcdma), the DCS transmissionsignal terminal T_(dcstx) and the DCS reception signal terminalT_(dcsrx). A control voltage is applied from a control terminal T_(ctl)5 to each of the FETs 31, 32 and 33 via resistances Rg. A controlvoltage is applied from a control terminal T_(ctl) 4 to each of the FETs21, 22 and 23 via resistances Rg. Similarly, a control voltage isapplied from a control terminal T_(ctl) 3 to each of the FETs 11, 12 and13 via resistances Rg. In addition, a bias voltage terminal T_(bias) isconnected to each of the terminals (source or drain) of the FETs 33, 23and 13 on their transmission/reception circuit sides via resistances R5,R4 and R3. Further, the bias voltage terminal T_(bias) is connected toterminals (drain or source) of the FETs 31, 21 and 11 on the filter 3side via a resistance Rb.

An FET in a non-saturation region behaves like a resistance, and thefact that the resistance value thereof changes with a gate voltage ismade use of. Near a turn-on voltage Vf, the impedance falls toapproximately several Ω and it comes to be in the on state, and at orbelow a pinch-off voltage Vp, it comes to be in the off state of a highimpedance with a capacitance of several hundred fF. Although occurrencesof distortion are likely even in handling large power with the FET whenit is in the off state, by multi-staging and connecting several FETs inseries as shown in drawing, it is possible to expand the handling powerin proportion to the square of the number of stages.

Incidentally, in the case of PIN diodes, when connected in multiplestages, a reverse bias potential is divided, and the handling power thuscannot be increaesd. The difference between a diode and an FET mainlylies in the fact that FETs are three-terminal devices, where as diodesare two-terminal devices, and that a gate voltage for on/off control isapplied to FETs. By connecting FETs in multiple stages, because theinput signal voltage can be divided between several FETs, while on theother hand the same gate voltage as that In the case of using a singleFET can be maintained for each of the FETs, it becomes possible toincrease the handling power without having the reverse-bias potentialvoltage divided. Thus, FETs are advantageous in that they can easily bemulti-staged such that the handling power may be increased.

Incidentally, although the high-frequency switch 4 may have an FETconfiguration like the high-frequency switch 50, because a controlvoltage of 5V would currently be required to handle GSM signals (morehigh-powered than others) with an FET configuration like thehigh-frequency switch 50, in the present mode, a diode configuration,which can handle GSM signals with a control voltage of 3V, is adopted.In addition, diodes D1 and D2 in the high-frequency switch 4 are turnedon at the time of transmission of the GSM signal, as described later,and hence, the problem of distortion occurring does not arise duringsignal transmission.

In FIG. 2, the status of a control signal of each of the switchingdevices of the switch apparatus of FIG. 1 and the correspondingswitching status are illustrated altogether as a table. As can beunderstood from this table, when transmitting with GSM on thehigh-frequency switch 4 side, a voltage of 3V is applied to the controlterminal T_(ctl) 2, and 0V is applied to T_(ctl) 1. As a result, both ofthe PIN diodes D1 and D2 come to be in the on state. Therefore, it isnow turned on between the GSM transmission signal terminal T_(gsmtx) andthe filter 2, and the GSM transmission signal is transmitted to theantenna terminal T_(ant) via the high-frequency switch 4, the filter 2and the diplexer 1. Incidentally, on the high-frequency switch 50 side,when no transmission is performed, by applying a voltage of 3V to thecontrol terminal T_(bias) and by applying 0V to T_(ctl) 3, T_(ctl) 4 andT_(ctl) 5, all of the FETs may be turned off. At this point, althoughpart of the GSM transmission signal reaches the high-frequency switch50, because it is attenuated to approximately 13dBm at the diplexer 1,the FETs in the off state do not give rise to distortion.

When transmitting with DCS on the high-frequency switch 50 side, avoltage of 3V is applied to the control terminals T_(bias), T_(ctl1) andT_(ctl) 4, and 0V is applied to T_(ctl) 2, T_(ctl) 3 and T_(ctl) 5. As aresult, the FETs 21, 22 and 23 come to be in the on state, and the otherFETs come to be in the off state. When GSM transmission is not performedsimultaneously with DCS, the PIN diodes D1 and D2 also come to be in theoff state. At this point, it is turned on between the DCS transmissionsignal terminal T_(dcstx) and the filter 3, and the DCS transmissionsignal is transmitted to the antenna terminal T_(ant) via thehigh-frequency switch 50, the filter 3 and the diplexer 1. Since themaximum transmission power of DCS is assumed to be 30dBm, this signalmay be applied to the other FETs 11, 12 and 13, as well as the FETs 31,32 and 33 in the high-frequency switch 5 without being attenuated.Therefore, although occurrences of distortion at the switching devicesmay be anticipated, because the handled power is expanded bymulti-staging the FETs in the present mode as mentioned above, it ispossible to suppress the occurrences of distortion. Incidentally,although part of the DCS transmission signal reaches the high-frequencyswitch 4, because it is attenuated by 20 dB or more at the diplexer 1,only approximately 10dBm is applied to the PIN diodes D1 and D2 evenwhen these diodes are in the off state, and no distortion occurs evenwith reverse-bias potentials of a low voltage (3V or less in the presentmode).

When transmitting with WCDMA on the high-frequency switch 50 side, avoltage of 3V is applied to the control terminals T_(bias), T_(ctl) 1and T_(ctl) 5, and 0V is applied to the control terminals T_(ctl) 2,T_(ctl) 3 and T_(ctl) 4. As a result, the FETs 31, 32 and 33 come to bein the on state, and the other FETs come to be in the off state. If GSMis not operated at the same time, the PIN diodes D1 and D2 also come tobe in the off state. Thus, it is turned on between the WCDMAtransmission/reception signal terminal T_(wcdma) and the filter 3, andthe WCDMA transmission signal is transmitted to the antenna terminalT_(ant) via the high-frequency switch 50, the filter 3 and the diplexer1. In this case, although occurrences of distortion at the FETs 11, 12and 13, and the FETs 21, 22 and 23 may be anticipated because themaximum transmission power of WCDMA is assumed to be 24dBm, it ispossible to suppress the occurrence of distortion because, as in thecase mentioned above, the handling power is expanded by multi-stagingthe FETs. In addition, although part of the WCDMA transmission signalreaches the high-frequency switch 4, because it is attenuated at thediplexer 1 by 20 dB or more, only approximately 4dBm is applied to thePIN diodes D1 and D2 in the off state, and no distortion occurs evenwith reverse bias potentials of a low voltage.

When receiving with GSM on the high-frequency switch 4 side, a voltageof 3V is applied to the control terminal T_(ctl) 3, and 0V is applied toT_(ctl) 2. As a result, the PIN diodes D1 and D2 come to be in the offstate. Thus, it is turned on between the GSM reception signal terminalT_(gsmrx) and the filter 2, and the GSM reception signal, which enteredfrom the antenna terminal T_(ant), is transmitted to the GSM receptionsignal terminal T_(gsmrx) via the diplexer 1, the filter 2 and thehigh-frequency switch 4.

When receiving with DCS on the high-frequency switch 50 side, a voltageof 3V is applied to the control terminals T_(bias) and T_(ctl) 3, and 0Vis applied to the control terminals T_(ctl) 4 and T_(ctl) 5. As aresult, the FETs 11, 12 and 23 come to be in the on state. Thus, it isturned on between the DCS reception signal terminal T_(dcsrx) and thefilter 3, and the DCS reception signal, which entered from the antennaterminal T_(ant), is transmitted to the DCS reception signal terminalT_(dcsrx) via the diplexer 1, the filter 3 and the high-frequency switch50.

When receiving with WCDMA on the high-frequency switch 50 side, avoltage of 3V is applied to the control terminals T_(bias) and T_(ctl)5, and 0V is applied to the control terminals T_(ctl) 3 and T_(ctl) 4.As a result the FETs 31, 32 and 33 come to be in the on state. Thus, itis turned on between the WCDMA transmission/reception signal terminalT_(wcdma) and the filter 3, and the WCDMA reception signal, whichentered from the antenna terminal T_(ant), is transmitted to the WCDMAtransmission/reception signal terminal T_(wcdma) via the diplexer 1, thefilter 3 and the high-frequency switch 50.

By a relatively simple circuit configuration of a switch apparatus asdescribed above, a small-sized switch apparatus, which performsswitching between signals of three or more systems, and which is capableof handling high-powered high-frequency signals with a relatively lowcontrol voltage, may be realized. In addition, since an antenna may beshared among three or more different communications schemes such as GSM,DCS and WCDMA, it becomes possible to configure a small-sized mobileterminal apparatus. Further, in each of the communications schemes GSM,DCS and WCDMA, since the PIN diodes D1 and D2 are in the off stateduring reception, a reduction in electric current consumption may berealized.

FIG. 3 shows another mode for carrying out the present invention. Thisis the switch apparatus shown in FIG. 1, wherein the high-frequencyswitch 50 is replaced with a high-frequency switch 51. Thehigh-frequency switch 51 is the high-frequency switch 50 to whichserially connected FET 41 through FET 43 are added between the T_(dcsrx)signal terminal and the ground as short circuit means. One end of theserially connected FET 41 through FET 43 is connected to the T_(dcsrx)signal terminal, and the other end is connected to a connection pointbetween the resistances Rb and R3 via a resistance R6, while beinggrounded via a capacitor C4. Isolation may be improved by applying 3V tothe gates of the FET 41 through FET 43 via the resistances Rg onlyduring DCS transmission, while applying 0V to the others.

Preferred modes for carrying out the present invention are describedabove, however, various modifications and changes other than thosementioned above are possible. For example, the control voltages of 0Vand 3V applied to the respective control terminals are not necessarilylimited to these values. Further, the number of stages of the seriallyconnected FETs is not limited to three stages, and the method ofconnecting the FETs is not limited to those illustrated in drawing.

According to the present invention, a small-sized switch apparatus,which is capable of handling high-powered high-frequency signals with arelatively low control voltage, and which switches between signal pathsof at least a first, second and third frequency bands, may be realizedwith a relatively simple circuit configuration without increasing thesize of a diplexer. In addition, since the antenna may be shared amongthree or more different communications schemes such as GSM, DCS andWCDMA, it becomes possible to configure a small-sized mobile terminalapparatus. Further, it is possible to simultaneously operate both of thesides (for instance, GSM and WCDMA or DCS and GSM) divided by thediplexer, and hence, a variety of system operations may be accommodated.

1. A switch apparatus for switching between signal paths comprising: adiplexer having a first signal terminal forming a transmission/receptionsignal terminal shared by signals of at least said first, second andthird frequency bands, a second signal terminal for outputting a signalof said first frequency band separated from a received signal, a thirdsignal terminal for outputting a remaining signal after said signal ofsaid first frequency band is separated, wherein said received signalinputted to said first signal terminal is divided between said secondand third signal terminals, and transmission signals to be inputted tosaid second and third signal terminals are combined and outputted tosaid first signal terminal; a first high-frequency switch connected tosaid second signal terminal of said diplexer; a second high-frequencyswitch connected to said third signal terminal of said diplexer, whereinsaid first high-frequency switch includes a plurality of switching meansrespectively configured with diodes for selectively switching betweentwo signal terminals for connection to said second signal terminal ofsaid diplexer, and said second high-frequency switch includes at leastthree switching means respectively configured with FETs for selectivelyswitching between at least three signal terminals for connection to saidthird signal terminal of said diplexer; and short circuit means havingserially connected FETs connected between one of said three signalterminals and electrical ground and having a terminal for receiving acontrol signal for controlling said serially connected FETs to connectsaid one of said three signal terminals to electrical ground.
 2. Theswitch apparatus according to claim 1, wherein each switching means ofsaid second high-frequency switch includes a plurality of seriallyconnected FETs.
 3. The switch apparatus according to claim 1 or 2,wherein said signals of said first, second and third frequency bands areglobal system for mobile communications, wide-band code divisionmultiple access, and digital cellular system signals, respectively. 4.The switch apparatus according to claim 3, wherein said firsthigh-frequency switch includes PIN diodes as said switching means andperforms switching between a global system for mobile communicationstransmission signal and a global system for mobile communicationsreception signal, and said second high-frequency switch includes threesets of serially connected multi-staged FETs as said switching means,and performs switching between wide-band code division multiple accesstransmission/reception signals, a digital cellular system transmissionsignal and a digital cellular system reception signal.
 5. (canceled)